store compact RSSI stats and skip real-time collection

Stats.WiFi is now map[string]int8 (json "wf") holding only available
RSSI
readings; SSID and unavailable signals stay in Info.WiFi. Averages are
rounded to whole dBm.

Wi-Fi is collected only on the default 60s interval; real-time requests
reuse the last snapshot to avoid spawning osascript / dumping the BSS
cache every second.

internal/site/src/components/routes/system/charts/wifi-chart.tsx

@@ -20,7 +20,7 @@ export function WiFiChart({
 	const dataPoints = interfaces.map(([id, current]) => ({
 		label: current.s ? `${id} (${current.s})` : id,
 		color: wifiColor(id),
-		dataKey: ({ stats }: SystemStatsRecord) => stats?.wifi?.[id]?.r,
+		dataKey: ({ stats }: SystemStatsRecord) => stats?.wf?.[id],
 	}))
 	return (
 		<ChartCard

internal/site/src/types.d.ts

@@ -91,7 +91,6 @@ export interface SystemInfo {
 }
 
 export interface SystemStats {
-	wifi?: Record<string, WiFi>
 	/** cpu percent */
 	cpu: number
 	/** peak cpu */
@@ -168,6 +167,8 @@ export interface SystemStats {
 	bat?: [number, BatteryState]
 	/** battery percentages by device name */
 	bats?: Record<string, number>
+	/** Wi-Fi RSSI (dBm) by interface */
+	wf?: Record<string, number>
 	/** network interfaces [upload bytes, download bytes, total upload bytes, total download bytes] */
 	ni?: Record<string, [number, number, number, number]>
 }